It doesn’t take much of this essential Southeast Asian condiment for the why-does-this-taste-so-good effect to kick in: a shake of the bottle into stews and sauces, a spoonful whisked into a vinaigrette, a drizzle over roasted vegetables or fried rice. (Why does it taste so good, you ask? Because umami.)

But it can be tricky, knowing how to choose from among the bottles of fish sauce written in various foreign scripts that you may or may not be fluent in.

For guidance, I called Andrea Nguyen, an authority on Vietnamese cooking and author of the forthcoming The Pho Cookbook, who as of this writing had 10 brands of fish sauce in her kitchen.

What is it?

Vats of fish—usually anchovies—are layered with salt and left to ferment for a year or longer, releasing a predictably potent, glutamate-rich liquid.

That liquid is fish sauce. In Vietnam, it’s called nuoc mam, in Thailand, it’s nam pla, and in the Philippines, it’s patis.

So, if you cook a lot of Thai food, a Thai fish sauce might make sense. If you’re looking for a universal, “very friendly” fish sauce, Vietnamese is a good bet, Nguyen says. Ultimately, it’s up to your palate.

What else is in fish sauce besides anchovies and salt?

Some brands add sugar or another sweetener and hydrolized wheat protein, a flavor enhancer. This isn’t necessarily a bad thing, says Nguyen.

“They’re there for a purpose. What the sugar and wheat extract do is round out the flavor of fish sauce. Without that little bit of sweet edge, it can be a little jagged and rough, like a piece of wood that needs sanding,” she says.

However, Nguyen doesn’t recommend fish sauce with preservatives such as sodium benzoate, which tend to leave a less-than-desirable aftertaste.

What else should I look for on the bottle?

The phrase “nuoc mam nhi.” This refers to the initial liquid extracted after a good, long fermentation—the base of the best fish sauce.

Some producers speed up the fermenting process so they can take that liquid, mix it with more salt and water, and pass it through the fish again, Nguyen says. The result: higher volumes of low-grade fish sauce.

It's also a good sign if you see “ca com" on the bottle: ca com are a specific type of anchovy that swim in Phu Quoc waters. But be wary of fish sauce labeled “Phu Quoc.” It's probably a cheap copycat of the real thing, which is hard to find.

Nguyen Thi Tinh, chairwoman of the Phu Quoc Fish Sauce Association, has been quoted by Vietnamese media as saying that 80 percent of fish sauce labeled “Phu Quoc" are counterfeit.

True Phu Quoc fish sauce, made from ca com anchovies, is a Protected Designation of Origin product, like Parmigiano-Reggiano and Champagne. It has to meet certain standards to be marked as such; PDO status isn't guaranteed for every producer in that region. The label should also say it was made and bottled in Phu Quoc, Vietnam.

How should I store fish sauce?

It's going to last a long time once opened, at least a year and up to two.

If you use it on a regular basis—for Nguyen, that's at least twice a week—you can store it in a cool, dark spot in your pantry. But it’ll taste best and stay freshest if kept refrigerated.

Over time and regular use, fish sauce will oxidize, turning darker and saltier. That’s natural, says Nguyen; just be sure to keep the lid shut tight.

“If it gets to smelling really funky or starts crystallizing, then you’ll want to start new,” she says.

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Thai-Style Squid and Cucumber Salad

The secret to cooking squid so it’s tender, not tough, is to cook it very quickly in small batches. Tossed with crunchy cucumbers, peanuts, and fresh red chiles, it makes a refreshing summer dinner spooned over rice or on its own.